建议楼主看文档，http://guides.rubyonrails.org/routing.html 解释：

The Rails router recognizes URLs and dispatches them to a controller's action. It can also generate paths and URLs, avoiding the need to hardcode strings in your views.

routes 是 rails 开始的第一步，controller 对路由请求做“处理”。view 和 model 是“被处理”的对象。

访问一个 url 时，routes 决定了处理这个 url 时所用 controller。